A sensor for detecting a light-transmissible foreign object, such as a raindrop, attached on a transparent body, such as a windowglass of a vehicle includes a light source, a light receiving unit disposed on the inside of the transparent body, and a prism fixedly attached on the transparent body on the...http://www.google.fr/patents/US4676638?utm_source=gb-gplus-shareBrevet US4676638 - Light-transmissible foreign object sensor
